1. Field of the Invention
The present invention relates to an imaging lens for solid-state image sensors for use in small imaging devices for use in small, thin electronic apparatuses such as mobile terminals, including cellular phones and mobile game machines, and personal digital assistants (PDAs).
2. Description of the Related Art
As the market for mobile terminals including an imaging device expands in recent years, a miniaturized solid-state image sensor having a high pixel number has been mounted on such imaging devices.
With such miniaturization and pixel number increase of image sensors, imaging lenses have been required to achieve higher performance such as higher resolution and higher image quality. Further, with their widespread use, imaging lenses have been required to be more low-cost.
To meet the higher performance requirements, imaging lenses including multiple lenses have been commonly used. Among others, there have been proposed five-lens imaging lenses that can achieve higher performance than three or four-lens imaging lenses.
JP-A-2007-264180 (Patent Document 1) discloses a high-performance-oriented imaging lens that includes: a first lens directing a convex surface toward the object side and having positive refractive power; a meniscus-shaped second lens directing a concave surface toward the image side and having negative refractive power; a meniscus-shaped third lens directing a convex surface toward the image side and having positive refractive power; a fourth lens having two aspheric surfaces, one of which is directed toward the image side and is concave near the optical axis, and having negative refractive power; and a fifth lens having two aspheric surfaces and having positive or negative refractive power. The first to fifth lenses are arranged in this order from the object side of the imaging lens.
JP-A-2007-298572 (Patent Document 2) discloses a high-performance-oriented imaging lens that includes: an aperture stop; a first lens having positive refractive power; a second lens bonded to the first lens and having negative refractive power; a meniscus-shaped third lens directing a concave surface toward an object side; a meniscus-shaped fourth lens directing a concave surface toward the object side; and a meniscus-shaped fifth lens having at least one aspheric surface and directing a convex surface toward the object side. The aperture stop and the first to fifth lenses are arranged in this order from the object side of the imaging lens.
JP-A-2010-262269 (Patent Document 3) discloses a higher-performance-oriented imaging lens that includes a first lens having positive refractive power; a second lens having negative refractive power; a third lens directing a convex surface toward the image side and having positive refractive power; a fourth lens having positive refractive power near the optical axis; and a fifth lens having negative refractive power near the optical axis. The first to fifth lenses are arranged in this order from the object side of the imaging lens. The image side surface of the fifth lens is concave near the optical axis and is a surface on which negative refractive power is weaker in a more peripheral area than in an area near the optical axis.
While the above-mentioned imaging lenses according to Patent Documents 1 to 3 include five lenses to increase performance, their long total lengths make it difficult to realize both their miniaturization and favorable aberration correction. The use of glass material also makes it difficult to reduce the cost.